Attention is directed to a commonly-assigned U.S. patent application by two of the inventors herein, Geis and Smith, Ser. No. 391,130, filed June 23, 1982, now U.S. Pat. No. 4,479,846, granted Oct. 30, 1984, entitled METHOD OF ENTRAINING DISLOCATIONS AND OTHER CRYSTALLINE DEFECTS IN HEATED FILM CONTACTING PATTERNED REGION hereby incorporated by reference.
Films of crystalline material are important in many areas of technology. In semiconductor electronics there is considerable interest in developing means of producing device-quality films of silicon (Si) and other semiconductors (especially the III-V compounds, HgCdTe and other infrared detectors) on insulating substrates such as SiO.sub.2. Foreign substrates having high thermal conductivity are also of interest. It is a goal of intensive current research to develop means of producing crystalline films on foreign substrates while ensuring that the crystallographic and chemical perfection of the films approaches that of bulk crystalline materials. In the application of crystalline films to solar photovoltaics, it is important that processes for producing said films be compatible with low cost mass production.
In recent years numerous investigators have produced large-grain polycrystalline films of Si on SiO.sub.2 by melting fine-grain polycrystalline Si using a laser, a strip-heater, or a bright lamp, and then allowing the melt to resolidify. The most effective techniques to date involve forming an elongated molten zone and scanning this zone across a film (see, for example, M. W. Geis, H. I. Smith, et al. "Zone-Melting Recrystallization of Si Films With a Movable-Strip Heater Oven", J. Electrochem. Soc. 129, 2812 (1982)). Some difficulties with current zone-melting recrystallization (ZMR) are: (a) in the absence of a single-crystal seed, a film will generally consist of many grains, each with a different orientation; and (b) within grains there are subboundaries and other defects distributed more-or-less randomly.
The copending application, Ser. No. 391,130 referenced above, describes a technique that solves difficulty (b). We have developed a planar constriction technique (H. A. Atwater, H. I. Smith, M. W. Geis, "Orientation Selection by Zone-Melting Silicon Films Through Planar Constrictions", Appl. Phys. Lett. 41, 747 (1982) which enables one to ensure that the film beyond the constriction is of a single orientation; a solution to difficulty (a). However, although the film has a single orientation, the particular orientation it has is not predictable or controllable. That is, the orientation can take on any value over a range (.+-..about.20.degree. in the case of Si ZMR).
It is an object of this invention to provide a means of selecting, predetermining or filtering the crystallographic orientation or orientations of a film.
It is a further object of this invention to utilize competition in growth from several distinct grains to accomplish this orientation filtering.
It is a further object of this invention to utilize patterns to induce orientation filtering.
It is a further object of this invention to obtain large grains of a selected orientation.